Sensing means

ABSTRACT

Apparatus for sensing movement of a member by feeding fluid, such as air, displaced as a result of movement of the member, to the control input jet of a fluid logic device so that the fluid logic device switches at a predetermined speed of movement of the member. A drilling apparatus in which the bluntness of the drill is monitored by such a movement sensing apparatus is described. The drilling apparatus also includes means for providing a pecking motion to the drill head.

United States Patent Alan T. Wright I [56] References Cited UNITED STATES PATENTS 10/1964 Reichertet al.

[72] Inventor 34 Llngl'ield Avenue, Fordhouses,

Wolverhampton, in the County of Stafford, 3,1 5 I ,505 3 396 631 21 Appl. No. 858,472

Primary Examiner- Francis S. Husar Attorney-Milton J. Wayne 8/l968 W0odward.............

[22] Filed Sept. 16, 1969 [45] Patented 7, 197K [32] Priority Sept. 17, 1968 rt n .ue mm m am ff 00 l e w mm a w d m; .m M r mu 3 S s a mh ac P w m inan 00 .m mm k V. Ab n i m8 r6 B H 3 0 4 G4 .1] 3] 33 [l of the member, to the control input jet ofa fluid logic device so that the fluid logic device switches at a predetermined speed of movement of the member. A drilling apparatus in [54] SENSING MEANS 13 Claims, 1 Drawing Fig.

which the bluntness of the drill is monitored by such a movement sensing apparatus is described. The drilling apparatus also includes means for providing a pecking motion to the drill head.

SENSING MEANS BACKGROUND OF THE INVENTION Field of the Invention This invention relates to means for sensing movement of a member.

BRIEF SUMMARY OF THE INVENTION An object of the invention is to provide a new and improved means for sensing movement of a member.

One aspect of the invention is means for sensing movement of a member comprising means for sensing speed of flow of fluid displaced in consequence of movement of said member wherein said means for sensing the speed of flow of fluid comprises conduit means feeding at least part of said fluid to the control input jet of a fluid logic element, said-element being arranged so as to switch at a predetermined speed of flow of said fluid.

The member may comprise the rotor of a rotary fluid motor, such as an air motor, and the fluid displaced may be the fluid exhausted from said motor.

Alternatively, the member may be the piston of a piston and cylinder fluid ram device, the fluid displaced being fluid displaced into or out of the cylinder as a result of relative movement between the piston and cylinder.

The fluid ram device may provide a feed means for a drill head.

The efficiency of drilling operations depends upon the speed of rotation of the drill bit, the pressure applied to the drill bit by the feed means to urge the bit against the workpiece, the characteristics of the workpiece which is being drilled and the sharpness of the drill bit.

During drilling operations the drill bit becomes blunt and hence the resistance to forward movement of the drill bit by the feed means increases and hence, when the feed means of the drill head is a fluid-operated device the rate of feed of the drill head decreases as the drill bit becomes increasingly blunt.

It is desirable for most forms of drilling to have a regular pecking" action incorporated into the drilling cycle. Pecking is a momentary reversing of the drilling followed by an immediate return to cutting. The purpose of this action is to clear swarf from the drilled hole and to allow penetration of any cutting fluid that may be used into the hole.

A more specific object of the invention is to provide a fluidoperated drilling apparatus wherein the drilling operation is interrupted when the drill bit reaches a predetermined degree of bluntness.

BRIEF. DESCRIPTION OF THE DRAWINGS A fluid-operated drilling apparatus embodying the present invention will now be described in more detail by way of example with reference to the accompanying drawing which is a diagrammatic representation of the pneumatic circuit of the drilling apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT A drill head, not shown, is connected to a piston rod attached to a piston 11 slidable in a cylinder 12. The drill head may be rotated by an electric motor or a pneumatic or hydraulic motor or by other suitable means.

Mains air under pressure is fed by supply valve means 14 and 17 to the cylinder 12 on one, forward, side of the piston 11 to cause the piston 11 to slide to the right in the Figure, to apply a feeding pressure to the drill bit to urge the drill bit against a workpiece to be drilled and, on the other, return, side of the piston 11 to cause the piston 11 to move to the left in the Figure to withdraw the drill bit from the workpiece.

A conduit 13 extends from one side of the piston 11 to a pilot operated spring return valve 14 to which lubricated air under pressure is fed from a source 9 via conduit 15. A conduit 16 leads from the valve 14 to the pilot input of a pilot operated spring valve 17. A conduit 18 leads from the valve 17 to the other side of the piston 11 in the cylinder 12.

Clean and dry mains air from a source 19 is fed via a pressure regulating valve 20, conduit 21 and filter 22 to the valve 17.

A conduit 23 leads from the valve 17 to a pilot operated spring valve 24 and a branch conduit 25 leads from the conduit 23 to the control input jet 26 of a monostable fluid logic element 27 and via a flow regulator 28 to the control input jet 29 of a second monostable fluid logic element 30. The conduit 25 exhausts to atmosphere through a second flow regulator 31.

An output of the fluid logic element 27 is connected via conduit 32 to the control input jet 33 of a third monostable fluid logic element 34 whilst an output of the fluid logic element 30 is connected via conduit 35 to the control input jet 36 of a fourth monostable fluid logic element 37. Clean dry mains air under pressure from a source 38 is fed via a pressure regulating valve 39 and conduit 40 to a manifold 41 and then by conduits 42 to the input side of the fluid logic elements 27, 30, 34, 37. The fluid logic elements 27, 30, 34, 37, are of turbulence amplifier type but other types of monostable element may be used if desired.

An output of the fluid logic element 34 is connected by conduit 43 to a step-up relay 44 whilst an output of the fluid logic element 37 is connected by conduit 45 to a second step-up relay 46. Clean dry mains air from a source 47 is connected to the step up relay by conduit 48 to provide a pilot signal to the valve 24 via conduit 49.

The step-up relay 44 is connected by conduit 50 to a pilot operated starting valve 51 to which clean dry mains air under pressure is fed from a source 52 by a conduit 53. The valve 51 is connected by conduit 54 to a confirm return" indicating device. A branch conduit 55 leads from the conduit 50 to a first mechanically operated spring-return valve 56 adapted to be operated by engagement of a member 8 movable with the drill head and a further conduit 57 leads from the output side of the valve 56 to a pilot operated first control valve 58. The first control valve 58 has a first air reservoir 59 connected thereto and lubricated mains air is fed to the first control valve 58 from a source 60 via conduit 61. A conduit 62 leads from an output port of the control valve 58 to provide a pilot signal for the valve 51. A branch 63 leads from the conduit 62 via a shuttle valve 64 to provide a pilot signal to the valve 14.

A conduit 65 leads from the shuttle valve 64 to a port of a pilot operated quick exhaust valve 66 and a branch conduit 67 leads from the conduit 65 to feed a pilot signal to the valve 66. A conduit 68 extends from the step-up relay 44 to the valve 66 and a branch conduit 69 provides a further pilot supply to the valve 66.

A conduit 70 extends from the conduit 65 via a flow control valve 71 to provide a pilot supply to a pilot operated spring second control valve 72 and a branch conduit 73 extends from the conduit 70, between the flow regulator 71 and the valve 72, to a second air reservoir 74.

A conduit 75 leads from an outlet port of the second control valve 72 to a shuttle valve 76. The conduit 75 also extends to a second mechanically operated spring return valve 77 to which lubricated mains air is fed from a source 78 via a conduit 79. Of course, air from the part of the conduit 75 leading from the second control valve 72, cannot enter the part of the conduit 75 leading from the shuttle valve 76 to the valve 77 because of the shuttle valve 76 which prevents communication between the two parts of the conduit 75.

A branch conduit 80 leads from the conduit 75 to provide a second pilot signal to the valve 51. A further branch conduit 81 leads from the shuttle valve 76 to provide a second pilot signal to the valve 58 and a branch conduit 82 connects a second shuttle valve 83 in parallel with the shuttle valve 76 and a conduit 84 provides a pilot signal to a valve 85 to which clean dry mains air is fed from a source 86 by a conduit 87. A conduit 88 is connected to a branch conduit 89 connected to the conduit 62 to provide a pilot signal to the valve 85 and a conduit 90 is connected to atmosphere.

A branch conduit 91 extends from the conduit 89 to manually operated valve 92 to which lubricated mains air is fed from a source 93 via conduit 94.

The way in which the drilling apparatus operated will now be described.

Assuming that the drilling apparatus is in a state prior to the start of a drilling cycle and this is the state shown on the circuit diagram. In this state the drill feed piston 1 1 is in its withdrawn position, i.e. fully to the left in the FIGURE and hence the valve 56 is actuated. The lubricated mains air fed from the source 9 to the valve 14 is fed through conduit 16 to apply a pilot signal to the valve 17 to actuate the valve 17 so that clean dry mains air from the source 19 is fed via pressure regulating valve 20, conduit 21, filter 22, valve 17 and conduit 18 to the return side of the piston 11.

No air enters the conduit 23 leading from the valve 17 and hence no signal is applied to the control input jets 26 and 29 of the fluid logic elements 27 and 30 and hence the clean dry mains air fed from source 38 via pressure regulating valve 39, conduit 40, manifold 41 and conduits 42 to the fluid logic elements 27 and 30 is undiverted and so air passes via the conduits 32 and 35 to the control input jets 33 and 36 respectively of the fluid logic elements 34 and 37 and hence the mains air fed to these fluid logic elements via the conduit 42 is diverted and hence there is no signal from the fluid logic elements 34 and 37 into the conduits 43 and 45 respectively and hence the step-up relays 44 and 46 provide no outputs.

As can be seen from the circuit diagram the lubricated mains air fed from source 95 to the second control valve 72 does not enter the conduit 75 because of the state of the second control valve 72.

The manually operated valve 92 is in a position so that lubricated mains air from the source 93 does not enter the conduit 91 and hence no pilot signal is applied to the valve 85 via the conduit 88 and hence the valve 85 is in position so that no pressure air is fed from the source 86 to the visual indicator via the conduit 96.

The first control valve 58 is in position so that lubricated mains air from the source 60 is connected to the reservoir 59.

The reservoir 74 is empty. The remaining pilot operated/spring return valves are in the spring return position.

In order to start the drilling cycle the manually operated valve 92 is actuated by pressing the plunger 97 thereof.

This causes the valve 92 to feed pressure air from the source 93 via the conduits 91 and 88 to the valve 85 to provide a pilot signal thereto to cause the valve 85 to pass pressure air from the source 86 via conduit 96 to the visual indicator.

The pressure air in the conduit 91 passes along conduit 89 and conduit 62 to provide a pilot signal to the starting 51 to cause the starting valve 51 to switch pressure air from the conduit 54 to the confirm return indicator into the conduit and hence into the branch conduit 55 also to the first mechanically operated valve 56 which is in its operated position due to the position of the piston 11. Thus the valve 56 feeds pressure air via the conduit 57 to provide a pilot signal to the first control valve 58 to cause the air under pressure in the reservoir 59 to pass via conduits 62 and 63 and shuttle valve 64 to provide a pilot signal to the valve 14. This pilot signal causes the valve 14 to switch mains air from the source 15 from the conduit 16 where it is providing a pilot signal to the valve 17 and instead into the conduit 13 to drive the piston 11 forwardly.

The output from the starting valve 51 via the conduit 50 also passes to the step-up relay 44 to provide a line input thereto.

The valve 17 also switches to connect the conduit 18 which feeds exhaust air from the withdrawal side of the piston 11 to the valve 17, to the conduit 23 and hence to the valve 24. In addition the exhausted air passes via the branch conduit 25 to the first fluid logic element 27 and also via the flow regulator 28 to the second fluid logic element 30.

As mentioned previously pressure air is continuously fed to the fluid logic elements 27 and 30 from the manifolds 41 and source 38 and when the exhaust from the cylinder 12 is connected to the conduit 25 is a signal is fed to the control input 26, 29, of the fluid logic elements 27 and 30 respectively causing the output of the element 27 to be taken from the conduit 32 thereby causing the third fluid logic element 34 to feed air to the conduit 43 because no air is fed to the control inputjet 33 thereof.

Thus the fluid logic element 34 causes a signal to be applied via conduit 43 to the step-up relay 44.

Similarly, the fluid logic element 30 causes the output to be taken from the control inputjet 36 of the fourth fluid logic element 37 so that a signal is applied by the fluid logic element 37 via the conduit 45 to the step up relay 46.

The step-up relay 44 is thereby caused to feed a pilot signal to the valve 14 via the quick exhaust valve 66 and shuttle valve 64 thereby holding the valve 14 in the position to drive the piston 11 forwardly. This occurs only after the signal from the first reservoir 59 of the first control valve 58 has bled to atmosphere through the flow regulator 98.

The main output from the step-up relay 44 is also directed via conduit 70 and flow control valve 71 to the second reservoir 74.

The step-up relay 46 switches a pilot signal to the exhaust valve 24 to cause the valve to switch to a position to exhaust the high pressure air in the conduit 23.

When the exhaust operation described in the last paragraph through the valve 24 has continued for a sufficient time to cause a drop in pressure between the flow regulators 28 and 31 to a level below the switching pressure required for fluid logic element 30 the element 30 will switch on" to feed a signal via the conduit 35 to the control jet 36 of the element 37 causing the fluid logic element 37 to switch off so that no air is fed by the conduit 45 to the step up relay 46.

It should be noted that a similar effect is not caused in relation to the fluid logic element 27 because a pressure differential exists on each side of the flow regulator 28 due to the flow regulator 31 being open to atmosphere. The value of this pressure differential is achieved by setting of the flow regulator 31.

The removal of the signal from the step-up relay 46 causes the valve 24 to close and hence the conduits 23 and 25 between the valve 17 and the fluid logic element 27 is no longer vented to atmosphere.

Assuming that the sharpness of the drill is such that the piston 11 can cause the drill head to be moved a speed above a desired minimum velocity then the following sequence of operation occurs.

Mains air from the step-up relay 44 continues to pass via the quick exhaust valve 66 and the flow regulator 71 to the second reservoir 74 within which the air slowly compresses until it reaches a pressure sufficient to overcome the spring of the second control valve 72 to cause the valve 72 to switch mains air from the source 95 into the conduit 75 to provide a pilot input through the valve 58 via the shuttle valve 76 and the conduit 81.

The time required to reach this switching point is dependent upon the setting of the variable flow regulator 71.

The switching of the first control valve 58 by the application of the pilot input via the conduit 81 causes the first reservoir 59 of the valve 58 to be charged from the mains source 60.

The pressure air in the conduit 25 is slowly vented to atmosphere via the flow control valves 28 and 31 until the air pressure falls below a level required to maintain the element 27 in its switched-off mode.

The time taken to reach this point is a function of:

l. The magnitude of the residual pressure left in the conduit 25 following the closing of valve 24 described hereinbefore.

2. The rate at which air escapes through the flow regulators 28 and 31 to atmosphere.

3. The rate at which air passes into the system due to the displacement from the return side of the piston 11 through the conduit 18 as the drilling operation proceeds. and,

4. The impedance to the air flow through the inputs to the fluid logic elements 27 and 30 (which is still effectively consuming air although below switching pressure).

Thus, the fluid logic element 27 switches on due to the fall in air pressure described above and this causes the third fluid logic element 34 to switch off so that pressure fluid is no longer fed via the conduit 43 to the step-up relay and hence the step-up relay 44 is also switched off.

The switching off of the step-up relay 44 stops flow of pressure fluid via the conduit 68 to the quick exhaust valve 66 thereby causing the signal to the second control vale 72 via the conduit 70 to be removed and to cause the air in the second reservoir "I4 to be exhausted rapidly to atmosphere via the quick exhaust valve 66.

This action also causes the second control valve 72 to no longer feed pressure air via conduit 75 shuttle valve 76 and conduit 8! to provide a pilot signal to the first control valve 58.

The valve 14 no longer has a pilot signal fed to it via the conduit 63 and hence the valve 14 switches its output signal from the conduit 13 to the conduit 16 to provide a pilot signal to the valve 17 causing the valve 17 switch mains air fed thereto from the source 19 via the pressure regulating valve 20 and conduit 21 and filter 22 to the conduit 18 to return the piston to the starting position shown in the figure.

The piston 11 continues to return until the external member on the drill mechanism actuates the valve 56 which in turn causes a pilot signal to be fed via the conduit 57 to the first control valve 58 causingthe air in the reservoir 59 of the valve 58 to be switched into the control system and to recommence the sequence of operations described above.

The sequence of operations for terminating the drilling action following the sensing of drilling feed speeds below a required minimum will now be described.

As the velocity of drill feed falls, due to increase in bluntness of the drill, the time taken for the air pressure in the conduit 25 to fall below the level required to maintain the fluid logic element 27 in the switched-ofi' mode becomes shorter until a time is reached whereat the element 27 will switch on and cause the element 34 to switch off the step-up relay 44 before the second reservoir 74 can be charged.

This situation will prevent the second control valve 72 feeding pressure air via the conduit 75 and shuttle valve 76 and conduit 81 to the first control valve 58 and hence the valve 58 will not be switched to the position which allows it to charge the first reservoir 59 and thus no air signal is available to recommence the automatic operation.

in addition, the valve 85 is not actuated because there is no output from the first control valve 72 to provide a pilot input signal to the valve 85 via conduits 75, 82, 84 and thus the visual indicator is maintained in its operated position, which denotes that the low pressure velocity has occurred.

The sequence of operations for terminating the drilling action at the end of a required drilling cycle will now be described.

When the total depth of hole drilled attains the required depth an external member on the drill mechanism actuates the second mechanically operated valve 77 which causes a signal to be fed via conduit 75 from pressure source 78 to the starting valve 51 to interrupt the supply of pressure air from the source 52 via the conduit 50 to the valve 56, thereby preventing automatic repetition of the drilling cycle as previously described.

At the same time the starting vale 51 switches on an output signal via conduit 54 to the confirm return indicator. The output from the valve 77 is also used via the shuttle valve 83 to actuate the valve 97 and remove the signal to the visual indicator.

It will be appreciated that the change in velocity of feed of the drill head with increasing bluntness of the drill is relatively small and that it is only by providing the fluid logic element as the sensing means that an efficient control system for the drilling apparatus can be achieved.

l claim:

1. Apparatus including means for sensing movement of a member comprising means for sensing speed of flow of fluid displaced in consequence of movement of said member wherein means for sensing the speed of fluid flow comprises conduit means to feed at least part of said fluid to the control input jet of a fluid logic element, said element being arranged so as to switch at a predetermined speed of flow of said fluid, said member being in the piston of a piston and cylinder fluid ram device, the fluid displaced being a fluid displaced into or out of the cylinder as a result of relative movement between the piston and cylinder, the ram device being a double acting ram device and there being fluid supply means including a fluid pressure pilot operated supply valve means to supply fluid under pressure to the cylinder on one, forward, side of the piston to move the piston forward or to feed fluid under pressure to the cylinder on the other, return, side of the piston to return the piston, conduit means to feed at least part of the fluid displaced from the return side of the cylinder when the piston is moved forwardly, to the control input jet of said fluid logic element and said fluid logic element being connected to said supply valve means whereby said fluid logic element provides a first pilot signal to the valve means to cause the valve means to feed fluid to the forward side of the piston when the speed of flow of fluid from the cylinder on said return side of the piston exceeds a predetermined speed or provides a second pilot signal to the valve means to cause the valve means to stop feeding fluid to said one side of the piston and to feed fluid to the return side of the piston, when the speed of fluid flowing from said return side of the cylinder does not exceed a predetermined speed.

2. Apparatus according to claim 1 wherein the piston is connected to a drill head and provides the feed means for the drill head.

3. Apparatus according to claim 2, including a first reservoir for fluid under pressure, first control valve means to connect said first reservoir to a source of fluid under pressure or to said supply valve means to supply said first pilot signal thereto, a second reservoir for fluid under pressure, means controlled by said fluid logic element to feed fluid to said second reservoir during forward movement of the piston to build up fluid pressure therein during forward movement of the piston, second control valve means whereby when the pressure of the fluid in the second reservoir exceeds a predetermined pressure a signal is passed to said first control valve means to cause said first control valve means to connect said first reservoir to said source of fluid under pressure and wherein said fluid logic element, after a predetermined time of forward movement of the piston, is arranged to deliver said second pilot signal to said fluid supply valve means to cause said supply valve means to feed fluid under pressure to the cylinder to return the piston and to cause said second reservoir to be exhausted whereby the signal fed by said second control valve means to said first control valve means is removed and wherein there is a first mechanically operated valve actuated by the piston on return movement thereof, to cause a signal to be passed to said first control valve means to cause said first reservoir to be connected to said supply valve means to supply said first pilot signal means to cause said supply valve means to feed fluid under pressure to the cylinder to move the piston forward.

4. Apparatus according to claim 3 wherein the output from sad fluid logic element is connected to the control input jet of a second fluid logic element.

5. Apparatus according to claim 4 wherein the output of the second fluid logic element is fed to a step-up relay.

6. Apparatus according to claim 4 wherein a further conduit extends from the conduit to the control jet of the first fluid logic element, via first and second flow control valves to atmosphere and wherein the control input jet of a third fluid logic element is connected to said conduit between said first and second flow control valves and wherein said third fluid logic element is arranged to feed a signal to an exhaust valve to cause said exhaust valve to connect said conduit to the first fluid logic element to atmosphere.

7. Apparatus according to claim 6 wherein the output of said first fluid logic element is connected to the control input jet of a fourth fluid logic element.

8. Apparatus according to claim 7 wherein the output of said fourth fluid logic element is connected to a step-up relay.

9. Apparatus according to claim 3 wherein the period required to charge said second reservoir is adjustable by means of an adjustable flow control valve connected in the fluid supply means to the reservoir.

10. Apparatus according to claim 3 wherein a manually operable valve is provided and arranged to feed a pilot signal to a starting valve means, said starting valve means being arranged to connect a source of fluid under pressure to said first mechanically operated valve whereby on operation of said manually operated valve said starting valve means causes fluid under pressure to be fed to said mechanically operated valve.

ll. Apparatus according to claim 10 wherein there is a second mechanically operated valve adapted to be actuated by the piston when the piston has caused movement of the drill head by a required amount to cause a pilot signal to be delivered to said third valve means to cause said starting valve means to disconnect said source of fluid under pressure from said first mechanically operated valve.

12. Apparatus according to claim 8 wherein the period required to charge said second reservoir is adjustable by means of an adjustable flow control valve connected in the fluid supply means to the reservoir.

13. Apparatus according to claim 12 wherein a manually operable valve is provided and arranged to feed a pilot signal to a starting valve means, said starting valve means being arranged to connect a source of fluid under pressure to said first mechanically operated valve whereby on operation of said manually operated valve said starting valve means causes fluid under pressure to be fed to said mechanically operated valve. 

1. Apparatus including means for sensing movement of a member comprising means for sensing speed of flow of fluid displaced in consequence of movement of said member wherein means for sensing the speed of fluid flow comprises conduit means to feed at least part of said fluid to the control input jet of a fluid logic element, said element being arranged so as to switch at a predetermined speed of flow of said fluid, said member being in the piston of a piston and cylinder fluid ram device, the fluid displaced being a fluid displaced into or out of the cylinder as a result of relative movement between the piston and cylinder, the ram device being a double acting ram device and there being fluid supply means including a fluid pressure pilot operated supply valve means to supply fluid under pressure to the cylinder on one, forward, side of the piston to move the piston forward or to feed fluid under pressure to the cylinder on the other, return, side of the piston to return the piston, conduit means to feed at least part of the fluid displaced from the return side of the cylinder when the piston is moved forwardly, to the control input jet of said fluid logic element and said fluid logic element being connected to said supply valve means whereby said fluid logic element provides a first pilot signal to the valve means to cause the valve means to feed fluid to the forward side of the piston when the speed of flow of fluid from the cylinder on said return side of the piston exceeds a predetermined speed or provides a second pilot signal to the valve means to cause the valve means to stop feeding fluid to said one side of the piston and to feed fluid to the return side of the piston, when the speed of fluid flowing from said return side of the cylinder does not exceed a predetermined speed.
 2. Apparatus according to claim 1 wherein the piston is connected to a drill head and provides the feed means for the drill head.
 3. Apparatus according to claim 2, including a first reservoir for fluid under pressure, first control valve means to connect said first reservoir to a source of fluid under pressure or to said supply valve means to supply said first pilot signal thereto, a second reservoir for fluid under pressure, means controlled by said fluid logic element to feed fluid to said second reservoir during forward movement of the piston to build up fluid pressure therein during forward movement of the piston, second control valve means whereby when the pressure of the fluid in the second reservoir exceeds a predetermined pressure a signal is passed to said first control valve means to cause said first control valve means to connect said first reservoir to said source of fluid under pressure and wherein said fluid logic element, after a predetermined time of forward movement of the piston, is arranged to deliver said second pilot signal to said fluid supply valve means to cause said supply valve means to feed fluid under pressure to the cylinder to return the piston and to cause said second reservoir to be exhausted whereby the signal fed by said second control valve means to said first control valve means is removed and wherein there is a first mechanically operated valve actuated by the piston on return movement thereof, to cause a signal to be passed to said first control valve means to cause said first reservoir to be connected to said supply valve means to supply said first pilot signal means to cause said supply valve means to feed fluid under pressure to the cylinder to move the piston forward.
 4. Apparatus according to claim 3 wherein the output from sad fluid logic element is connected to the control input jet of a second fluid logic element.
 5. Apparatus according to claim 4 wherein the output of the second fluid logic element is fed to a step-up relay.
 6. Apparatus according to claim 4 wherein a further conduit extends from the conduit to the control jet of the first fluid logic element, via first and second flow control valves to atmosphere and wherein the control input jet of a third fluid logic element is connected to said conduit between said first and second flow control valves and wherein said third fluid logic element is arranged to feed a signal to an exhaust valve to cause said exhaust valve to connect said conduit to the first fluid logic element to atmosphere.
 7. Apparatus according to claim 6 wherein the output of said first fluid logic element is connected to the control input jet of a fourth fluid logic element.
 8. Apparatus according to claim 7 wherein the output of said fourth fluid logic element is connected to a step-up relay.
 9. Apparatus according to claim 3 wherein the period required to charge said second reservoir is adjustable by means of an adjustable flow control valve connected in the fluid supply means to the reservoir.
 10. Apparatus according to claim 3 wherein a manually operable valve is provided and arranged to feed a pilot signal to a starting valve means, said starting valve means being arranged to connect a source of fluid under pressure to said first mechanically operated valve whereby on operation of said manually operated valve said starting valve means causes fluid under pressure to be fed to said mechanically operated valve.
 11. Apparatus according to claim 10 wherein there is a second mechanically operated valve adapted to be actuated by the piston when the piston has caused movement of the drill head by a required amount to cause a pilot signal to be delivered to said third valve means to cause said starting valve means to disconnect said source of fluid under pressure from said first mechanically operated valve.
 12. Apparatus according to claim 8 wherein the period required to charge said second reservoir is adjustable by means of an adjustable flow control valve connected in the fluid supply means to the reservoir.
 13. Apparatus according to claim 12 wherein a manually operable valve is provided and arranged to feed a pilot signal to a starting valve means, said starting valve means being arranged to connect a source of fluid under pressure to said first mechanically operated valve whereby on operation of said manually operated valve said starting valve means causes fluid under pressure to be fed to said mechanically operated valve. 